One of the Trump administration’s latest environmental rollbacks could have major implications for public health, climate change and water quality in the Chesapeake Bay region.
The U.S. Environmental Protection Agency on Feb. 12 finalized a repeal of its “endangerment finding” for several greenhouse gases, including carbon dioxide. The 2009 finding states that greenhouse gases “threaten the public health and welfare of current and future generations.”
The repeal effectively removes the legal underpinning for federal climate policy, including regulating emissions from vehicles and power plants.
At the same time, the EPA rescinded all federal greenhouse gas emission standards applying to highway vehicles and engines.
Calling it “the single largest deregulatory action in U.S. history,” EPA Administrator Lee Zeldin argued that repealing the endangerment finding would give American consumers a freer hand over the kinds of vehicles they can buy. The EPA estimates that the Obama-era finding has cost consumers more than $1 trillion in the vehicle and engine sector alone.
Opponents of the repeal say the move is contrary to the law, long-established science and the effort to fight climate change. Several environmental and public health groups have filed suit to overturn the action, and more legal challenges are expected.
Supporters of the endangerment finding in the Chesapeake Bay region worry that its repeal could have harsher consequences here than in many other parts of the country. That’s because the region is considered the most vulnerable to sea level rise on the East Coast, and many of its urban areas face a disproportionately high risk of being sickened by air pollution.
Environmentalists are also concerned that the repeal could set back the Bay cleanup.
Efforts to reduce pollution in the Bay and to battle climate change are intricately connected, experts say. Heating the planet causes the atmosphere to hold more moisture. The heavier rains that follow are expected to dislodge more sediment, leading to more silt and nutrient pollution in the Bay.
Warmer waters also hold less oxygen, making them more susceptible to “dead zones,” where virtually all aquatic life that can’t flee dies.
In that sense, the future health of the Bay depends on reducing greenhouse gas emissions, said Quentin Scott, federal policy director for the Chesapeake Climate Action Network.
“We have to address the root causes of climate change, and the endangerment finding repeal makes addressing those root causes much more difficult,” Scott said. Without the finding as the legal foundation, federal greenhouse gas rules are reduced to “at-will” regulations that can be more easily overturned by courts, he added.
In 2007, the Supreme Court ruled that the government could regulate greenhouses gases under the Clean Air Act, paving the way for the EPA to make the endangerment finding two years later. The nation’s highest court declined to intervene in 2013 after the DC Circuit court knocked down several challenges against it.
The “best scientific information available” shows that greenhouse gases “contribute significantly” to air pollution, said Christopher Hoagland, director of the Maryland Department of the Environment’s air program, on behalf of his agency in written comments last year when the repeal was still pending.
Rachel Lamb, MDE’s assistant secretary for climate policy, called the administration’s decision “in contrast to everything we understand about the state of the science.” She suggested that the state could seek “other strategies,” perhaps including new regulations, to address greenhouse gas reductions required by state law.
In Maryland, the transportation sector accounts for 35% of the state’s greenhouse emissions, the largest of any sector, Hoagland noted in his letter. He expressed concern that the repeal would jeopardize Maryland’s ability to require cleaner vehicle emission standards than what the federal government mandates.
Maryland is one of 17 states that have adopted California’s stricter vehicle emissions regulations under an EPA waiver. The list includes four others in the Chesapeake watershed: Delaware, New York, Pennsylvania and Virginia.
Under Democratic Gov. Wes Moore, Maryland in 2023 signed on to California’s updated standards, which require all passenger cars and light trucks to be electric vehicles by 2035. The waiver’s status is currently in litigation, though, after the Republican-controlled Congress passed a Congressional Review Act resolution revoking it in January 2025.
An MDE analysis at the time suggested that the new California vehicle regulations would result by 2040 in an additional reduction of 6,000 tons of nitrogen oxide (NOx) compared to the previous requirements. Carbon dioxide emissions were also expected to decline by 82 million metric tons from vehicular and power plant sources.
The new state restrictions would lead to a healthier public, the MDE report asserted, estimating about $40 million in annual health benefits from decreases in respiratory and cardiovascular illnesses and from fewer lost workdays.
An anonymous EPA spokesperson said that repealing the endangerment finding would not harm public health, pointing to the same models used by “previous administrations and the climate zealots.” The change, the person added in their statement to the Bay Journal, also has no effect on the ongoing regulation of “traditional” air pollutants, such as nitrogen.
Air regulations don’t just make people healthier; they can make the Bay healthier as well, scientists say. Airborne nitrogen that falls back to the earth or directly on the water’s surface accounts for about one-third of that nutrient in the Bay.
About half of that airborne nitrogen typically leaves tailpipes and smokestacks as Nox. The other half is in the form of ammonia, mostly from agriculture. From 1985 to 2015, federal air regulations helped reduce the amount of nitrogen entering the Bay from NOx emissions by an estimated 60%, research shows.
“Such a huge proportion of our [Bay cleanup] progress has come from the air deposition and NOx,” said Joe Wood, a Virginia-based senior scientist for the Chesapeake Bay Foundation. “If you roll back some of those NOx emissions regulations, it has huge implications on our capacity to not just save the Bay but break even.”
Keith Eshleman, a scientist with the University of Maryland’s Center for Environmental Science’s Appalachian Laboratory who has extensively studied air pollution impacts on water quality, is less certain that the repeal will significantly alter the cleanup.
The vehicle and power plant industries have been on pollution-cutting trajectories for so long, he said, it will likely take them a long time to change course, assuming they choose to do so. “This may be a bump in the road. It may be a hiatus,” Eshelman said. “But it’s not the end of making that transition.”
Further, after years of successfully reining in atmospheric nitrogen, there just isn’t that much more progress to be made on that front for the Bay, he said. According to computer modeling conducted for the Bay cleanup in 2024, a nationwide net-zero cap on carbon dioxide emissions from all sectors by 2050 would only lower nitrogen in the Bay from airborne sources by 5%.